1. Field of the Invention
This invention relates to a method and apparatus for generating and intermittently dispensing a saturated vapor of an active liquid in an inert carrier gas under pressure.
The invention is specially applicable to gassing said cores used in metal casting and will be described in this context by way of illustration.
2. Description of the Prior Art
In making sand cores, by the "cold box" method, a foundry mix is first prepared by mixing with sand a combination of binder substances, for example an isocyanate and a phenolic resin. The foundry mix is deposited in a sand hopper above the coring machine. Increments of sand are packed, on demand, into the core box cavity to mold a green core supported by the walls of the core box. A vapor containing an amine curing agent is passed through the core to cure the binder to form a self-supporting body. Air is finally passed through the core to purge it of excess amine vapor.
Several methods have been used to pass the curing vapor into the sand core. In some of these, the amine is entrained in an air stream, using metering pumps, oil lubricators, syphon arrangements or spray nozzles. The amine must be vaporized and diffused through the air stream while it is in motion. In this system, the gassing times tend to be lengthened because of poor or uneven diffusion. Also, non-vaporized liquid amine may remain in the air stream and be deposited in the sand and, as the hot metal is later poured, outgassing will occur, i.e. gas will be evolved from the amine liquid and cause porous castings. Further, since the amine is usually introduced into the air stream a few feet from the core box, it is impossible, in the limited time period (less than one second), to attain close to satisfactory concentration of amine. Should an attempt be made to add more amine, in this short interval, the added amine will not have time to vaporize and some of it will be deposited (as a liquid) in the sand core with resultant outgassing. Precautions must also be taken because of the flammability of the amine-air mixture. In addition, because of the short space of time between the introduction of the liquid amine to the air stream, and its entering the sand core, these methods can only handle relatively small cores.
A further expedient has been to use a prefilled syphon-type cylinder filled with high pressure (say 750 psig at 70.degree. F.) mixture of liquid amine and liquid carbon dioxide. A valve on this cylinder is fitted with a syphon tube which goes to within a short distance from the bottom of the cylinder. The vapor pressure above the liquid in this case forces the mixture of liquid amine and liquid CO.sub.2 up through the syphon tube through a vaporizer and then through a pressure reducing regulator. Since a proportion of the amine tends to recondense it has been usual to pass the mixture through a second vaporizer and then to the core. This procedure has limitations. Due to the corrosive nature of amine, the only available regulators are corrosive service stainless steel regulators. These regulators are basically designed for very low volume dispensation, thus placing a limited capacity on both core size and high speed cycling.
Attempts to obtain an amine-rich vapor by bubbling air or gas through a perforated pipe or screen immersed in liquid amine creates bubbles too large to effectively pick up enough amine to sustain high speed coring. Also, the agitation of large bubbles allows droplets of liquid amine to be entrained with the air or gas stream, again resulting in porous castings.